Winsock API: listen

参考MSDN:http://msdn.microsoft.com/en-us/library/windows/desktop/ms739168(v=vs.85).aspx

The listen function places a socket in a state in which it is listening for an incoming connection.

Syntax

int listen(

  _In_  SOCKET s,

  _In_  int backlog

);

Parameters

s [in]
A descriptor identifying a bound, unconnected socket.

backlog [in]
The maximum length of the queue of pending connections. If set to SOMAXCONN, the underlying service provider responsible for socket
s will set the backlog to a maximum reasonable value. There is no standard provision to obtain the actual backlog value.

Return value

If no error occurs, listen returns zero. Otherwise, a value of
SOCKET_ERROR is returned, and a specific error code can be retrieved by calling

WSAGetLastError.

Remarks

To accept connections, a socket is first created with the
socket function and bound to a local address with the
bind function. A backlog for incoming connections is specified with
listen, and then the connections are accepted with the
accept function. Sockets that are connection oriented, those of type
SOCK_STREAM for example, are used with listen. The socket
s is put into passive mode where incoming connection requests are acknowledged and queued pending acceptance by the process.

A value for the backlog of SOMAXCONN is a special constant that  instructs the underlying service provider responsible for socket
s to set the length of the queue of pending connections to a maximum reasonable value.

Example Code

The following example demonstrates the use of the listen function.

#ifndef UNICODE
#define UNICODE
#endif

#define WIN32_LEAN_AND_MEAN

#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdio.h>

// Need to link with Ws2_32.lib
#pragma comment(lib, "ws2_32.lib")

int wmain()
{

//----------------------
// Initialize Winsock
WSADATA wsaData;
int iResult = 0;

SOCKET ListenSocket = INVALID_SOCKET;
sockaddr_in service;

iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
if (iResult != NO_ERROR) {
wprintf(L"WSAStartup() failed with error: %d\n", iResult);
return 1;
}
//----------------------
// Create a SOCKET for listening for incoming connection requests.
ListenSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (ListenSocket == INVALID_SOCKET) {
wprintf(L"socket function failed with error: %ld\n", WSAGetLastError());
WSACleanup();
return 1;
}
//----------------------
// The sockaddr_in structure specifies the address family,
// IP address, and port for the socket that is being bound.
service.sin_family = AF_INET;
service.sin_addr.s_addr = inet_addr("127.0.0.1");
service.sin_port = htons(27015);

iResult = bind(ListenSocket, (SOCKADDR *) & service, sizeof (service));
if (iResult == SOCKET_ERROR) {
wprintf(L"bind function failed with error %d\n", WSAGetLastError());
iResult = closesocket(ListenSocket);
if (iResult == SOCKET_ERROR)
wprintf(L"closesocket function failed with error %d\n", WSAGetLastError());
WSACleanup();
return 1;
}
//----------------------
// Listen for incoming connection requests
// on the created socket
if (listen(ListenSocket, SOMAXCONN) == SOCKET_ERROR)
wprintf(L"listen function failed with error: %d\n", WSAGetLastError());

wprintf(L"Listening on socket...\n");

iResult = closesocket(ListenSocket);
if (iResult == SOCKET_ERROR) {
wprintf(L"closesocket function failed with error %d\n", WSAGetLastError());
WSACleanup();
return 1;
}

WSACleanup();
return 0;
}